1,842 research outputs found
The ellipticities of Galactic and LMC globular clusters
The globular clusters of the LMC are found to be significantly more
elliptical than Galactic globular clusters, but very similar in virtually all
other respects. The ellipticity of the LMC globular clusters is shown not be
correlated with the age or mass of those clusters. It is proposed that the
ellipticity differences are caused by the different strengths of the tidal
fields in the LMC and the Galaxy. The strong Galactic tidal field erases
initial velocity anisotropies and removes angular momentum from globular
clusters making them more spherical. The tidal field of the LMC is not strong
enough to perform these tasks and its globular clusters remain close to their
initial states.Comment: 3 pages LaTeX file with 3 figures incorporated accepted for
publication in MNRAS. Also available by e-mailing spg, or by ftp from
ftp://star-www.maps.susx.ac.uk/pub/papers/spg/ellip.ps.
On commuting varieties of nilradicals of Borel subalgebras of reductive Lie algebras
Let be a connected reductive algebraic group defined over an
algebraically closed field \mathbbm k of characteristic zero. We consider the
commuting variety of the nilradical of
the Lie algebra of a Borel subgroup of . In case acts
on with only a finite number of orbits, we verify that is equidimensional and that the irreducible components are in
correspondence with the {\em distinguished} -orbits in . We
observe that in general is not equidimensional, and
determine the irreducible components of in the
minimal cases where there are infinitely many -orbits in .Comment: 10 page
On commuting varieties of parabolic subalgebras
Let be a connected reductive algebraic group over an algebraically closed
field , and assume that the characteristic of is zero or a pretty good
prime for . Let be a parabolic subgroup of and let be
the Lie algebra of . We consider the commuting variety . Our main
theorem gives a necessary and sufficient condition for irreducibility of
in terms of the modality of the adjoint action of
on the nilpotent variety of . As a consequence, for the case a Borel subgroup of , we give a classification of when is irreducible; this builds on a partial classification given
by Keeton. Further, in cases where is irreducible, we
consider whether is a normal variety. In particular,
this leads to a classification of when is normal.Comment: 19 pages; minor update
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